Rice DNA-Binding One Zinc Finger 24 (OsDOF24) Delays Leaf Senescence in a Jasmonate-Mediated Pathway

Leaf senescence is the final stage of leaf development and in cereal crops, the timing of senescence relative to grain filling has major effects on agronomic traits such as yield. Although many genetic factors are involved in the regulation of leaf senescence in cereals, the key regulators remain to be determined. Plant transcription factors with a conserved DOF (DNA-binding one zinc finger) domain play roles in multiple physiological processes. Here, we show a novel function for OsDOF24 as a repressor of leaf senescence in rice (Oryza sativa). In wild-type leaves, OsDOF24 expression rapidly decreased during natural senescence (NS) and dark-induced senescence (DIS). The gain-of-function mutant osdof24-D, which contains an enhancer-trap T-DNA in the OsDOF24 promoter, exhibited delayed leaf yellowing during NS and DIS. Transgenic plants overexpressing OsDOF24 showed the same phenotype during DIS. Reverse-transcription quantitative real-time PCR analysis revealed that senescence-associated genes (Osl85, Osl57 and OsNAP) and chlorophyll degradation genes (NYC1, NYC3 and SGR) were downregulated in the osdof24-D mutant during dark incubation. Among the phytohormones, only methyl jasmonate induced OsDOF24 expression. Furthermore, the reduced expression of jasmonate biosynthesis-related genes (OsLOX2, OsLOX8, OsHI-LOX, OsAOS1 and OsAOS2) in osdof24-D decreased endogenous jasmonate levels, resulting in delayed leaf senescence under DIS conditions. Yeast one-hybrid assays showed that OsDOF24 binds to the promoter region of OsAOS1. Taken together, our results demonstrate that OsDOF24 suppresses the induction of leaf senescence during vegetative growth by deactivating jasmonate biosynthetic pathways.